Too late to reply for your initial visit but if you come again, don't miss the Rose Gardens which are spectacular (roses are out about late May through late August) and is easily accessible by public transportation (bus). Also, there is the Pittock Mansion (you'd need transportation to reach it unless you know the walking route above Knob Hill).
Also, on Thursday, the Portland Mounted Police give a tour of their stables which are right on the waterfront and easily accessible by foot or bus or street car from downtown. All the horses are half draft-horse and just beautiful. Sadly, this wonderful program is on the budget chopping block.